Nonconducting substances such as surfaces of plastic films, paper webs, or plastic fibers may develop an electric charge at the surface by coming in contact with other substances or due to rapid separation from one another, and the resulting electric voltage on such surfaces may reach a few megavolts. “Natural” unassisted charge removal may take a few hours to days, depending on atmospheric humidity, the type of material and the magnitude of the electric charge.
The electric charge buildup on surfaces may also result in a disturbance in the systems used as well as constitute a health risk to people working on these systems in the production and/or processing of those surfaces. Furthermore, handling is much more difficult due to the electric charge on the surface and the resulting electrostatic forces, in particular in the case of plastic films, paper webs, or plastic fibers, such as those widely used in the packaging industry.
To minimize the surface charge buildup, it is known from the related art that charge removal devices which blow ionized air over the charged surface may be used. Due to the resulting increase in conductivity of the air, a rapid charge removal with a resulting residual voltage of typically a few kV is achieved, depending on the boundary conditions. The limit of a few kV depends on the particular method used, because a voltage of several kV is necessary for ionization of air and/or process gases used as an alternative.
A device for producing a plasma and in particular for treatment or activation of surfaces has been proposed in unpublished German Patent Application No. 199 43 953, where microstructure discharges are produced by injection of microwaves into a hollow conductor provided with through-bores with simultaneous supply of gas. Therefore, a locally limited or planar gas plasma prevails in the vicinity of the through-bores in the particular plasma regions.